The present invention relates to a multifunctional reference electrode having both temperature and voltage sensing elements in the same device for use in an electrochemical cell. More particularly, the invention relates to a sensing device in which a hollow half-cell electrode serves as the housing for temperature sensing means to measure the temperature of the half-cell thereby permitting a precise correlation between temperature and voltage. The reference electrode has been designed for use in high temperature lithium-aluminum/metal sulfide cell systems but has other uses as hereinafter set forth.
In the development of a lithium-aluminum/metal sulfide cell, it is important that a known reference electrode potential be generated by an electrical double layer in the reference electrode with which to measure the potential difference between the reference electrode and the electrode of interest. At a cell operating temperature of about 400.degree. C., temperature variations across the cell in the order of about 50.degree. C. have been detected, thereby causing the voltage of the half cell with respect to the electrode of interest to vary considerably. The change in voltage, if undetected, prevents an effective determination of cell voltages under various conditions of cell operations. For example, temperature effects may cause the cell voltage to change by values in the order of at least 12 mV, while it is important to detect changes in the cell voltage on the order of 3-4 mV with an accuracy of about 1 mV. Since voltage of these cells is temperature dependent, it is essentially impossible to measure and calculate the potential of the electrode of interest without precise knowledge of the reference electrode temperature.
The multifunctional reference electrode of the present invention has been used in the development and design of the lithium-aluminum/metal sulfide battery. The reference electrode is also useful in the development of any battery as well as having other applications such as for pH electrodes, indicator electrodes, and the like in various fields of industrial processes, environmental control and research.
Heretofore, no device has been available which will precisely measure the temperature of the reference electrode in the area where the electrode potential is produced. The reference electrode of the present invention provides extremely accurate temperature measurements at the surface where the electrode potential is produced, thereby permitting accurate calculations for the electrode of interest.